The passage suggests that which of the following is a prediction concerning meteor streams
A. Dust particles in a meteor stream will usually be distributed evenly throughout any cross section of the steam.
B. The orbits of most meteor streams should cross the orbit of the Earth at some point and give rise to a meteor shower.
C. Over time the distribution of dust in a meteor stream will usually become denser at the outside edges of the stream than at the center.
D. Meteor showers caused by older by older meteor streams should be, on average, longer in duration than those caused by very young meteor streams.
E. The individual dust particles in older meteor streams should be, on average, smaller than those that compose younger meteor streams.
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Which of the following best describes the relation of the first paragraph to the passage as a whole?
A. It makes a general observation to be exemplified.
B. It outlines a process to be analyzed.
C. It poses a question to be answered.
D. It advances an argument to be disputed.
E. It introduces conflicting arguments to be reconciled.
技工室复制模型采用的印模材料为
A. 印模膏
B. 印模蜡
C. 硅橡胶
D. 藻酸盐印模材料
E. 琼脂印模材料